System for controlling the operation of refrigeration units



. y 3, 1950 F. M. JONES 2,509,099

SYSTEM FOR CONTROLLING THE OPERATION 0F REFRIGERATION uurrs Filed June 30, 1947 3 Sheets-Sheet 1 IE. I

WW flrraews y 1950 F. M. JONES 2,509,099

CONTROLLING THE OPERATION SYSTEM FOR OF REFRIGERATION UNITS Filed June 30, 1947 3 Sheets-Sheet? FITIDE/Y May 23, 1950 F M JONES 2,509,099

SYSTEM FOR 'CdNTRbLLING THE OPERATION OF REFRIGERATION unrrs Filed June 50, 1947 SSheets-Sheet 5 m vmme FREDEmcK MJONES Patented May 23, 1950 7 SYSTEM FOR CONTROLLING THE OPERA- TION OF REFRIGERATION UNITS Frederick M. Jones, Minneapolis, Minn., asslgnor to The U. S. Thermo Control (30., Minneapolis,

Minn a corporation of Minnesota Application June so, 1941, Serial No. 758,053

13 Claims. (01. 62-4) My invention relates to an improved system for controlling the operation of a refrigeration unit. In refrigeration systems to which the present invention is applicable, the air within an enclosure is continuously cooled by forcibly bringing the air into contact with a cold surface such as an evaporator through which a refrigerant medium is circulated. If the temperature of the refrigerant is substantially lower than that of the air which is brought into contact with the surface of the evaporator, moisture which is present in the air will condense on the evaporator and congeal in the form of a layer of frost or ice. As the congealed layer increases in thickness, it will tend again on the interior of the enclosure after the defrosting operation has been completed.

In the prior art it has been customary in the case of refrigeration units of this class to terminate the circulation of air at the same time that the circulation of the refrigerant medium is stopped in order to periodically remove the accumulation of frost from an evaporator. In some instances it has also been customary to circulate a heated medium through the evaporator to more quickly melt the frost. The handicap of the prior art practice has been that after the defrosting operation was completed the delivery of refrigerant medium and the circulation of air were resumed simultaneously and if there were any remaining drops of moisture on the evaporator the same were picked up and carried by the air stream before the refrigerant medium had an opportunity to cool the evaporator to a point where this moisture was congealed.

Another and more important handicap of the prior art has been that the defrosting operation has been a time controlled operation which is impractical when the thickness of the layer of frost is likely to differ from day to day or from one application to another. When the frost is removed by circulating a heated medium through the evaporator and a definite time cycle is provided for the defrosting operation one of several undesirable situations may arise. In one instance the layer of frost may be of greater thickness than normal and under these conditions the period for which the timer has been set may be inadequate for a complete defrosting. In another instance the layer of frost may be of lesser thickness than normal and under these conditions the heating period will extend beyond the time required to melt the frost and the enclosure or space which is being cooled will itself become heated. This latter condition is by far the most dangerous condition, for if the enclosure contains frozen foods or other perishable products there is likelihood of their being thawed which will result in spoilage.

Furthermore, where the accumulation was rapidly removed by circulating a heating medium through-the evaporator, the ice would fall from the evaporator in large pieces, and would tend to accumulate beneath the evaporator to either form a source from which the air could pick up moisture or would form a mass which would not melt readily during the short time required for a defrosting operation.

Inthe present invention, the circulation of refrigerant medium and air are simultaneously stopped at regular periodic intervals and definite steps are taken to improve the removal and disposal of the accumulated frost or ice during the defrosting operation. Another feature is that after the defrosting operation has been completed the refrigerant medium is permitted to return to the evaporator for a sufiicient length of time so as to completely congeal any remaining moisture on the surface of the evaporator prior to the time that the circulation of air is resumed. A further and more important step, however, is that the defrosting operation which may be started by a time controlled mechanism, is terminated by a tem perature controlled device. By this arrange ment, should the layer of frost be abnormally thin, the defrosting operation cannot be permitted to extend for such a period as to heat the refrigerated enclosure and cause damage to the materials stored therein.

In the present invention an evaporator in the form of a continuous coil is connected in a conventional refrigeration system containing an expansion valve which controls the flow of an evaporable fluid to the coil from whence the expanded vapors are removed in the usual manner by a compressor. During the normal operation of the system, an electric motor operated blower or fan circulates the air which is present in an enclosure such as a refrigerator cabinet, over and about the coils to cool the air and maintain a constant temperature within the enclosure. As the air contains a certain amount of moisture, the act of bringing it into contact with the cold coil will cause moisture in the air to precipitate on the coil and congeal in the form of a layer of frost or ice. Since the layer of frost tends to insulate the coil and reduce its effectiveness, steps must be taken periodically to remove the frosted layer from the coil.

In general, it is advisable to periodically defrost the coil during those hours when the enclosure or refrigerator is not being frequently opened. As for example if the enclosure is used for containing a supply of frozen foods in a grocery store, it is advisable to defrost the coil before the beginning of and after the close of the business day. To this extent, a time controlled mechanism is set to perform the defrosting operation at predetermined intervals.

To accomplish the defrosting operation, the coil is provided with a conduit connected to the condenser and the high pressure side of the-compressor so that compressed heated gases may be admitted to the coil which will cause the frost or ice to quickly melt. The flow of these heated gases to the coil is controlled by a valve which is normally closed during the refrigeration cycle and which is moved to an open position by the time controlled mechanism. When the time controlled mechanism actuates the valve it simultaneously de-energizes the fan to stop the circulation of air over the coil to thus prevent dispersing the melted portion of the frost as it is formed. A container is provided in combination with the coil and situated beneath the coil to receive the defrosted accumulation which drops from the coil. As there is likelihood of chunks of ice or frost falling from the coil into the container, an electrical heater is provided within the container and is energized each time the defrosting operation takes place so as to melt the ice for quick disposal of the resulting liquid to the sewer or the like.

The act of defrosting the evaporator is terminated by a temperature responsive device which is positioned adjacent the evaporator and responds to a rise in temperature of the evaporator which occurs after the heated gases completely melt or remove the frost from the coil. Through suitable circuit means the temperature responsive device moves the valve controlling the flow of hot gases to-its closed position shortly after V the frost has been removed whereafter when the pressure of the gases in the evaporator is reduced, the refrigeration cycle re-commences. The time controlled mechanism is set to resume the operation of the fan after a period of time which would under any normal set of circumstances be sufiicient for the defrosting operation to be complete and the coil to again be completely cooled to the extent that any remaining moisture would be congealed.

An object of my invention is to provide a control system for periodically controlling the defrosting of an evaporator of a refrigeration unit.

Another object is to provide a system for controlling the defrosting of a refrigeration evaporator wherein the defrosting operation is initiated by a time controlled device and terminated by'a temperature controlled device.

Another object is to provide in combination with a refrigeration system having means for defrosting the evaporator thereof by circulating a heating medium through the evaporator, a con- 4 trol system for periodically admitting the heat ing medium to the evaporator to defrost the evaporator and means for terminating the flow of heating medium as soon as the evaporator is defrosted.

Another object is to provide an electrical control system for periodically operating the various elements of a refrigeration system in order to periodically free the system of an accumulation of frost or ice.

Another object is to provide a system for controlling the defrosting of a refrigeration evaporator in such a manner that a plurality of elements perform one function simultaneously and thereafter certain of said elements are made to perform another function sequentially in timed relationship to the operation of other elements.

Another object is to provide in combination with a refrigeration system means for periodically removing an accumulation of ice thereon and means for disposing of said accumulation.

Another object is to provide in combination with a refrigeration system having an electric valve for controlling the flow of a heated fluid to an evaporator and an electric fan for blowing air over the evaporator, a control system for operating the valve and the fan so that the evaporator may be periodically defrosted whereby the valve and fan are respectively rendered operative and inoperative simultaneously until the evaporator is defrosted and thereafter the operation of the fan is initiated subsequent to the operation of the valve.

A further object is to provide a two-position, time-controlled switching device for use with condition control apparatus which when moved to one of its positions terminates operation of one portion of the apparatus and initiates the operation of another portion of the apparatus, whose operation is in turn terminated by a temperature responsive switch prior to the period when the time-controlled switch is moved to its other position.

Other and further objects may become apparent from the following description and claims, I

Fig. 2, is a schematic diagram of a refrigeration system to which the invention is applied;

Fig. 3, is a schematic diagram of a modification of the system shown in Fig. 1:

Fig. 4, is a front elevation of a time-controlled switching device used in controlling the system shown in Fig. 3, with portions broken away: and,

Fig. 5, is a partial view of the rear of the structure shown in Fig. 4.

Referring now to the several figures of the drawing, the invention will be explained in detail.

Referring to Fig. 2 in conjunction with Figs. 1 and 3 is schematically shown a refrigeration system with which the present invention is applied. Indicated by reference numeral 6 is a refrigerant compressor driven by a prime mover indicated at l. The prime mover 1 may be either an electric motor or an internal combustion engine, but in either instance, its operation is controlled in response to conditions existing within a. space whose temperature is to be controlled. The high pressure side of compressor 6 is connected by a conduit 9 to a condenser 8. An evaporator Ill, which is normally positioned in a space to be cooled has its inlet end [2 connected by a conduit l3 to a receiver 15. Conduit i3 contains an expansion valve l4. which is controlled by a thermostatic bulb 14c that is secured to the evaporator. The valve I 4 controls the flow of refrigerant fluid from the receiver II to the evaporator III. A conduit l3a connects the outlet of the condenser 8 to the receiver It. At its other end It evaporator I is connected by a conduit H to the inlet orlow pressure side of compressor 5. A conduit l9 extends from conduit 5 between compressor 6 and condenser 8 to an electric valve and thence to a junction 2| with evaporator It for conducting hot refrigerant gases to the evaporator.

A container 24 is positioned beneath the evaporator ID for receiving the defrosted accumulation either as ice or water, which falls from the evaporator while the same is being defrosted. Container 24 is provided with a connection 25 which leads to a sewer or other suitable place of liquid disposal. Mounted within container 24 is an electrical heater 25 which is provided to melt any chunks of ice which fall into container 24 during the defrosting operation.

Mounted on one side of evaporator III is a-fan 28, which is operated by an electric motor and is provided to circulate air from within an enclosure over and about the evaporator. On the other side of the evaporator is a thermostat casing 21 which is supported by fins 29 extending between the coils of the evaporator in such a manner that the casing is affected by the temperature of the evaporator.

Valve 20, motor 30, thermostat casing 21, and heater 26 all have electrical cables extending therefrom to a control box indicated at 3| for controlling the operation of these several devices in a manner which is schematically shown in Figs. 1 and 3.

Referring now to Figs. 1 and 3, valve 20 is shown as a, solenoid operated valve having an induction coil 32 and a movable armature 34, which when attracted by coil 32 moves a plunger to permit the flow of fluid through valve 20. The thermostat is here illustrated as a bi-metallic element 36 which when subjected to a rise in temperature is adapted to move to the left as shown in the drawings and engage a contact 38.

Electrically associated with thermostat 56 is. a solenoid operator or relay 40 having an induction coil 42 which at one end thereof is connected to contact 38 bya conductor 44 and which is also joined to a holding contact 46. A movable arma- .6 and the other end of coil 22 is Joined to conductor It by branch 82. A branch 24 Joins one end of 'resistor 25 and conductor II.

The operation of the refrigeration plant shown in Fig. 2 will be briefly explained. The evaporator Ill and container 24 are located in a space whose temperature is to be cooled while the prime mover, compressor and condenser are located elsewhere. The prime mover I which may be either an electric motor or an internal combustion engine is controlled in a customary manner by the temperature of the controlled space, and in normal operation is intermittently operated according to the demand of the-controlled space. When, however, the evaporator becomes coated with frost, its cooling capacity is reduced to such a degree that the space is constantly requiring additional cooling and, therefore, the prime mover would normally be in operation. If on the other hand the temperature in the controlled space were sufficiently low, so as not to be demanding operation of the prime mover and compressor, then when the defrosting operation started the radiant heat from heater 26 which is energized during the defrosting operation would radiate sufllcient heat so that in a short time a demand for cooling would occur. Thus during the defrosting operation the compressor will always be in operation. It should also be under-- stood that when the defrosting operation starts and hot gas is admitted to the evaporator, the expansion valve l4 will close and remain closed. Valve l4, which is a commercial product, contains a safety diaphragm which positively closesthe source of power 64 through conductor 66,

ture 50 having a spring 5| attached thereto is connected to a switch arm 52 which is adapted to normally engage a contact 54.

A time-controlled switching device indicated by general reference numeral 56 is provided with a movable switch arm 58 which is adapted to engage either of contacts 50 or 52 at predetermined intervals.

The elements mentioned heretofore are electrically connected by a circuit which includes a source of power 64 from which extends a conductor 66, that at one end is joined to switch arm',

and coil 42 of relay 40. A short conductor 80 joins conductor 14 with one end of coil 32 of valve 20 switch blade 58, contact 60, conductor 68, motor 30, and conductor It back to the source of power. Valve 20 is closed and' the expansion valve i4 will in a conventional manner be operative to permit compressed fluid to pass from receiver I5 through inlet 12 of evaporator M where it is expanded to give a cooling effect and withdrawn by compressor 6 and therefore evaporator III is at a low temperature so that the air circulated by fan 28 is being cooled. Timer 56 is adjusted to periodically defrost evaporator l0 and assuming that the time for defrosting has arrived, switch blade 58 is moved by a timing means, one of which is to be explained in detail hereinafter,

from'its full line position in engagement with contact Gil into its dotted line position in engagement with contact 62. Movement of the switch blade in this manner breaksthe circuit to motor 30 and the fan 28 ceases to rotate. When switch blade 58 engages contact 62, valve 20 i energized and moved to an open position to admit hot gases from condenser 8 as well as compressor 6, through conduits 9 and Hi, to the junction 2 I, where it enters evaporator l0. Simultaneously the resistance heater 26 is energized to assure the removal of any frost or congealed moisture which may be present in container 24 or which may drop into container 24 from evaporator i0.

(5 This operation brought about by a circuit 7 which may be traced as follows: from the source of power 84 through conductor, switch blade I8, contact 82, conductor 12, switch blade 82, contact 54, conductor 14, heater coil 28, branch 84, and conductor ll back to the source of power. Simultaneously branch 88 conducts current from conductor 14 through coil 82 to branch 82 which branches are connected in parallel with heater 28. when coil 82 is energized armature 84 moves upwardly to open valve 28 to admit the heated fluid as set forth above. As evaporator I8 is heated by the hot gases, the ice or frost will fall into container 24 and be further melted by heater 28 whence the accumulation will be disposed of through conduit 25. As evaporator I8 is freed of ice it will be further heated by the hot gases and thermostat 88, which is positioned in heat transfer relationship with evaporator l4 and which will respond to a slight rise in temperature, moves to the left as shown in Fig. 1 until it engages contact 88. when this has occured, a circuit will be established through the thermostat 36 which may be traced as follows: from conductor 72 (which is still conveying current as previously explained) through branch 16, thermostat 88, contact 88, conductor 44, coil 42, and branch 18 to conductor 18. Energization of coil 42 causes armature 58 and switch arm 52 to move downwardly breaking engagement with contact 54 and engaging the holding contact 46. When switch blade 52 is moved in the manner described, the circuit'previously described to coil 32 of valve 28 and heater 25 are simultaneously broken and valve 28 is caused to move to its original closed position. After valve 28 has closed, the compressor 6 Will commence to reduce the pressure within evaporator I0 and evaporation of fluid admitted by expansion valve l4 will be resumed, and in a short time the evaporator is again cooled.

As the evaporator is again cooled, thermostat 85 will move to the right under the influence of the descending temperature causing it to separate from contact 38. This action, however, will have through relay 48 which may be traced as follows:

from source of power 64, conductor 68, switch 1 blade 58, contact 82, conductor 12, switch blade 52, holding contact 46, coil 42, conductor 18 and conductor 10 back to the source of power.

In actual practice the time required to defrost evaporator i8 is a variable factor ranging from about 5 to minutes depending on the thickness of the ice formed thereon, but timer 56 is normally set to return switch blade 58 from its dotted line position to its full line position in about minutes as this is more than an ample amount of time to assure complete defrosting and recooling of the evaporator under any normal condition. When, therefore, switch blade 58 is returned to its full line position, the circuit to relay 48 is broken and a circuit to motor 30 is re-established. When the relay circuit is broken,

switch blade 52 is moved by spring means 5| into engagement with contact 54 to complete the operation.

Referring now to Fig. 3, substantially the same arrangement exists as was described in the case of Fig. 1 except that relay 40 in this case is 'not provided with a holding contact 48 and in place thereof a mechanical arrangement operated by timer 56 is used to assure the proper movement of switch blade 52. In Fig. 3 switch blade 52a. is shown as being connected to a tension spring 88 which normally biases the switch blade to an open circuit position. The relay 48 has its armature 58 connected to a latching mechanism 88 which when the relay 48 is de-energized, holds switch blade 52a in engagement with contact 54. However, when the relay is energized by thermostat 36, the latching mechanism drops to permit spring 86 to move arm 52a. away from contact 54. This action then breaks the circuit through thermostat 86 and the latching mechanism springs back to engage the outer end of arm 52a and hold it away from contact 54. A. crank which is operated by a mechanical connection 92 from the timing mechanism 56 is' provided for restoring switch blade 52a to its normal position in a manner to be described hereinafter,

The operation of the system shown in Fig. 3 is as follows: when switch blade 58 of timer 58 is moved to its dotted line position in engagement with contact 82 a circuit is establishedwhich may be traced as follows: from the source of power 54 through conductor 68, switch blade 58, contact 82, conductor I2, switch blade 52a, contact 54, conductor 14 to the coil 32 of valve 28' and the resistor 26 in container 24 and back to the source of power through conductor 10 as explained in the operation of Fig. 1.

As explained in conjunction with the operation of Fig. 1, hot gas is permitted to pass from conduit 9 through the conduit l9 past the valve 20 and thence through the junction 2| into the evaporator after which it is returned to the compressor through conduit H. The hot gases act to melt or loosen the frost on the evaporator, which together with any chunks of ice, fall into the container 24 and are melted by the heater 26. After defrosting is completed, the heat emitted from the evaporator will cause the thermostat 35 to move to the left, as shown in the drawing, and engage contact 38. When this occurs, a circuit is established from conductor 14, through branch 16a, thermostat 36, contact 38, conductor 44, coil 42 of the relay 40, and conductor 18 back to conductor 78 to energize the relay 48. When relay 40 is energized, armature 58 which is connected to the latch 88, moves in a downwardly direction so that the latch is brought below the end of blade 52a. Spring 86 is then permitted to move the switch blade 52a away from the contact 54 to thereby break the circuit and deenergize relay 48, so that in efiect relay 40 is only momentarily-energized to permit latch 88 to be moved downwardly so that spring 86 may break the circuit. As soon as relay 40 is de-energized, spring 5i causes the outer end of latch 88 to move upwardly and engage the lower end of switch 52a to hold the same in an open position until timer 56 acts to move switch blade 52a into engagement with contact 54. The switch closing operation is performed by the complex mechanical connection represented at 92 together with crank 90 which is first caused to move in a counter-clockwise direction to close the switch and then in a clockwise direction to move away from the switch. When actuated the switch 52a is moved so that" its outer end is beyond the outer end of latch 88 and in engagement with contact 54, thereby permitting the latch 88 to move to the position shown in Fig. 3 where it latches the switch blade 52a in a closed position. During the interval of time that switch 52a is away from contact 54, the evaporator will have been cooled and the thermostat 88 will have moved away from contact 38 so that 28 the circuit to the relay will be open. Also during this time the expansion valve I4 will have opened to permit liquid refrigerant to circulate again through the evaporator in the normal cooling cycle. Thereafter the timer 99 will move the switch blade 59 away from contact 92 and into engagement with contact 99 to reinitiate the operation of motor 89 and fan blade 28.

Referring now to Figs. 4 and 5, timer 98, relay 49 and other features forming a practical combined control device are shown in detail. Reference numeral 95 indicates a panel on one side of which is mounted a conventional synchronous clock motor (not shown). Extending from the motor is a shaft 99 on which is mounted a dial 98 that is marked off as shown in Fig. 4 in 24 hours. Also mounted on shaft 99 are a pair of actuating levers I99 and I9I which are adapted to successively engage studs I92 on dial I94 at periods determined by the setting of levers I99 and I9I. A shaft I99, which carries a time indicating pointer I9l on its outer end, extends from dial I94 through panel 95 and on its other end carries a wheel I98, Fig. 5, which has a plurality of ratchet teeth II9 located on its periphery. Also mounted on shaft 99 are a second pair of actuating levers H2 and II9 which carry abutments I I4 that are adapted to engage a cam follower 9| on a curved crank 99 which is pivotally mounted on panel 95 at II5. Crank 99 carries a detent II9 and an actuating member I I1 whose functions will be described hereinafter. A lever II8 having a flat end II9 is supported on panel 95 at I 29 to engage studs I22 on the opposite side of dial I94, which are in all respects similar to studs I92. Lever H8 is held in engagement with each stud I22 as dial I 94 is rotated by a spring I24 and acts to prevent further rotation of the dial.

Relay 49 is disclosed as a conventional electromagnetic relay having a coil 42, an armature 99, and an armature spring I. Mounted on the front of panel 95 and shown in Fig. 4 is a conventional snap switch I29 having a push button actuator I28 which is schematically shown in Fig. 3 as members 52a and 54. Mounted on the top of snap switch I29 is a flexible member I39 which is adapted to be engaged by actuator M1 on crank 99 to depress the push button I28 of switch I29 and also to abut armature 59 of the relay 49 and to hold the armature either open or closed.

Positioned on the rear of panel 95 as shown in Fig. 5 is a movable switch arm 58 having an extension 59 which contacts the outer surface of wheel I98. Suitably supported on either side of switch 58 are contacts 58a and 58b which are adapted to alternately engage either contact 99 or contact 92.

The operation of the device shown in Figs. 4 and 5 will now be explained in detail. Levers I99 and H2 are utilized to initiate one defrosting operation and levers WI and H3 are utilized to initiate another cycling defrosting operation. In Fig. 4 the two levers forming each set of levers are widely separated from each other for purposes of illustration, but in actual practice lever H2 would be positioned just slightly in back of lever I99 and lever II3 would be similarly positioned with relation to lever I9I. These levers are nested on shaft 99 with levers H2, H3 being positioned under or in back of levers I99 and I9I. The pointer I9! is a stationary member and merely indicates the existing time on dial 98. Levers I99 and IN start the cycling operation and levers I I2 and H3 perform a double function 19 which will be explained hereinafter. In view of the foregoing explanation, lever IN is shown in the act of engaging one of the four studs I92 on dial I94 and moving the same in a counter clockwise direction until one of the four studs I22 has depressed lever H8 and is engaged in detent I I9 of lever 99. While this is occurring, wheel I98 is also being rotated and at the point where stud I22 is engaged in detent II9, the follower 99, which is biased against the periphery of wheel I98 so as to hold contact 58a in engagement with contact 99, snaps into a notch II9 thereby separating contact 980 from contact 99 and bringiigg contact 98b into engagement with contact Member I39 is normally depressed against push button I28 in which position snap switch I29 is in a closed circuit position and the end of member I39 is abutting the end of armature 99 which is in a raised or non-attracted position thus forming a completed circuit arrangement as shown in Fig. 3, permitting the defrosting operation to proceed as previously explained.

As the operation of the clock motor and shaft 99 continues, lever II3 brings abutment II4 into engagement with the cam follower 9I of crank 99 and crank 99 is made to rotate counter-clockwise on its pivot II 5.

However, since the functioning of lever H3 is set to take place at a short timed interval after the functioning of lever I9I, it may be assumed that during the interim coil I9 will have been defrosted and thermostat 39 will have engaged contact 38 to actuate the relay 49. When armature 59 is attracted by coil 42, the armature will move to the left as shown in Fig. 4 and in so doing, member I39, which has been heldin a depressed position by the armature, will spring upwardly releasingpush button I28 and permitting snap switch I29 to move to an open circuit position.

Returning now to the function of lever II3 and crank 99, as crank 99 is moved downwardly, stud I22 is released from detent II9, and dial I94 which (by means not shown) is spring biased to move in a counter clockwise direction for a quarter turn until the next stud I22 is engaged by portion II9, of lever II8. However, the dial I94 moves sufliciently forward to cause the follower 59 to be raised to the periphery of wheel I98 in a sudden action thus breaking the engagement between contacts 58b and 92, and making engagement between contacts 58a and 99 to resume the original circuit to fan motor 39. Crank 99, however, continues to move downwardly until abutment III engages member I39 and moves member I39 beyond the end of armature 59 whereupon the push button I28 of switch I29 is again depressed and armature 59 is raised by spring 5i thus preparing relay 49 and switch I29 for another operation. Thereafter abutment II4 on lever H3 is moved clear of cam follower 9I and crank 99 returns in a clockwise direction to its raised position by spring means (not shown) and a cyclic operation is completed.

The advantages of my invention will be apparent from the preceding discussion, but as numerous changes may occur to those skilled in the art, my invention is defined in the terms of the appended claims.

I claim:

1. In combination with a cooling unit upon the exterior surface of which a progressive frost ac cumulation occurs, means for defrosting said cooling unit comprising, a source of heat, a medium for transferring energy from said source of heat,

a conductor for transferring said medium from the source of heat to the cooling unit, flow control means cooperable with said conductor for regulating the flow of said medium through said conductor, an electric operator for actuating said flow control means to initiate the flow of said medium to said cooling unit, means for controlling the operation of said electric operator, comprising a circuit including said electric operator, said circuit being adapted for connection to a source of power, a two-position switch in said circuit which when moved to one of its positions effects energization of said electric operator, and another switch in said circuit, said latter switch having a temperature responsive portion positioned in heat transfer relationship with Said cooling unit and responsive'to a rise in temperature of said cooling unit, said latter switch being effective to de-energize said electric operator after the frost accumulation is removed from said cooling unit to thereby terminate the flow of said medium through said conductor.

2. In combination with a cooling unit upon the exterior surface of which a progressive frost accumulation occurs, means for defrosting said cooling unit comprising, a source of heat, a medium for transferring energy from said source of heat, a conductor for transferring said medium from the source of heat to the cooling unit, flow control means cooperable with said conductor for regulating the flow of said medium through said conductor, an electric operator for actuating said flow control means to initiate the flow of said medium to said cooling unit, means for controlling the operation of said electric operator, comprising a circuit including said electric operator, said circuit being adapted for connection to a source of power, a two-position switch in said circuit which when moved to one of its positions effects energization of said electric operator, and a normally inactive switch in said circuit, said latter switch having a temperature responsive portion positioned in heat transfer relationship with said cooling unit and responsive to a rise in temperature of said cooling unit, said latter switch being effective to de-energize said electric operator after the frost accumulation is removed from said cooling unit to thereby terminate the flow of said medium through said conductor.

3. In combination with a refrigeration system having a high pressure side and a low pressure side, a conduit extending between said sides for conducting hot gas from the high pressure side to the low pressure side to defrost the outer surface of the low pressure side, a valve connected to said conduit which When opened permits the passage of hot gas to the low pressure side, an electric actuator for said valve, a circuit including said electric actuator and which is adapted for connection to a source of power, a switch in said circuit which when closed eil'ects energization of said actuator, and a normally inactive switch Joined to said circuit and having a temperature responsive portion positioned in heat transfer relationship with the low pressure side, said latter switch being adapted for movement to an active position to de-energize said actuator when heat from the gas is radiated from the low pressure side.

-4. In combination with a cooling unit upon the exterior surface of which a progressive frost accumulation occurs, means for defrosting said unit comprising, a source of heat, a medium for transferring energy from the source of heat, a

conductor for transferring said medium from the source of heat to the cooling unit, flow control means connected to the conductor for controlling the flow of said medium through said conductor, an electric operator for actuating said flow control means to initiate the flow of said medium to the cooling unit, means for controlling said electric operator comprising a circuit including said operator, said circuit being adapted for connection to a source of power, a two-position switch in said circuit which when moved to one of its positions effects energization of said operator, a normally closed switch in said circuit which when opened de-energizes said operator, a relay operatively connected to said normally closed switch, and a thermostatic switch connected to said relay and having a temperature responsive portion positioned in heat transfer relationship with said cooling unit for actuating said relay upon a change of temperature adjacent said cooling unit.

5. In combination with a cooling unit which is adapted to receive a progressive accumulation of frost on its outer surface, a fan for circulating air in contact with the outer surface of the cooling unit, an electric operator for driving the fan, means for defrosting said unit comprising, a source of heat, a medium for transferring energy from said source of heat, a conductor for transferring said medium from the source of heat to the cooling unit, flow control means connected to the conductor for controlling the flow of said medium through said conductor, an electric operator for actuating said flow control means to initiate the flow of said medium to the cooling unit, means for controlling the operation of said first and said second electric operators comprising, a circuit including said operators, said circuit being adapted for connection to a source of power, a first two-position switch in said circuit which when moved to one of its positions opens the circuit to said first operator and instantly effects energization of said second operator, and a second two-position switch in said circuit which when moved to one of its positions while the first named switch is in said one position, opens the circuit to said second operator.

6. In combination with a cooling unit which is adapted to receive a progressive accumulation of frost on its outer surface, a fan for blowing air into contact with the outer surface of said cooling unit, an electric operator for driving the fan, means for defrosting said unit comprising, a source of heat, a medium for transferring energy from the source of heat, a conductor for transferring said medium from the source of heat to the cooling unit, flow control means connected to the conductor for controlling the flow of said medium through said conductor, a second electric operator for actuating said flow control means to initiate the flow of said medium to the cooling unit, means for controlling the first and second electric operators comprising a circuit including said operators, said circuit being adapted for connection to a source of power, a first two-position switch in said circuit which when moved from a first position to a second position de-energizes said first named operator and effects energization of said second named operator, a second two-position switch in said circuit which when moved to one of its positions while the first named switch is in its second position deenergizes said second operator, a relay operatively connected to said second switch, and a third two-position switch connected to said relay and 13 having a temperature responsive portion positioned in heat transfer relationship to the cooling unit, said third switch being operative to ac-- tuate the relay upon a change of temperature in the space ambient the cooling unit.

7. In combination with a refrigeration coil, means for circulating a refrigerant fluid through said coil, a fan for circulating air in contact with the outer surface of the coil whereby a progressive accumulation of frost is deposited thereon, an electric operator for driving said fan, means for defrosting the coil comprising a source of heat, a medium for transferring energy from the source of heat, a conductor for transferring said medium from the source of heat to the coil, a flow control means connected to said conductor for controlling the flow of said medium, a second electric operator for actuating said fiow control means, means for controlling the first and second electric operators to terminate circulation of air and initiate flow of said medium to said coil comprising a circuit including said first and second electric operators, said circuit being adapted for connection to a source of power, a first two-position switch in said circuit which when moved from a first position to a second position efiects de-energization of said first named operator and energization of said second named operator, a normally closed switch in said circuit which when opened while the first named switch is in said second position de-energizes said second named operator, a relay operatively connected to said normally closed switch which when energized opens said switch, a second twoposition switch connected to said relay and when closed energizing the same, said second switch having a temperature responsive portion positioned in heat transfer relationship with the coil and closing in response to a rise intemperature ambient to the coil, and a timer for holding said first two-position switch in said second position for a period normally greater than is required for the temperature of the medium to actuate said second two-position switch.

8. In combination with a refrigeration system I having a coil, means for circulating a refrigerant medium through said coil, an electric fan which when energized circulates air into contact with said coil, means for conducting a heated medium to said coil, an electric valve connected to said latter means and when energized admitting said heated medium to said second named means, and means for controlling the operation of said valve and said fan which comprises, a circuit including said fan and said valve, two-position switch in said circuit and adapted to alternately connect saidfan and said valve with a source of power, timing means operable to periodically move said switch from a first position to a second position and to return said switch from said second to said first position after a predetermined period of time, said switch when moved from said first to said second position being operative to deenergize said fan and energize said valve, a normally closed switch in the circuit to said valve, a solenoid operator in said circuit which when energized moves said normally closed switch to an open circuit position to de-energize said valve, a normally open temperature responsive switch electrically joined to said solenoid operator and positioned adjacent said coil, said switch being adapted to close upon a rise of temperature adjacent said coil, and means associated with said solenoid operator for maintaining the energization of said operator until said timing means 14 triliovea said two position switch to said first posi- 9. In combination with a refrigeration plant having a high pressure side and a low pressure side, means for circulating a cooling fluid from the high pressure side to the low pressure side, a fan for blowing air into contact with the low pressure side, an electric operator for driving said fan, a conduit for conducting hot gas from the high pressure side to the low pressure side, a valve connected to said conduit for controlling the flow of said gas, an electric actuator for said valve, means for actuating said fan and said valve comprising a circuit including said first and said second electric actuators, a two-position switch in said circuit which when moved to a first position de-energizes said first named operator and effects energization of said second named operator, a timer for periodically moving said switch to said one position for a predetermined period of time, and means including a temperature responsive switch in said circuit for superseding the timer and de-energizing said second named operator prior to the time that said timer moves said two-position switch to a second position to effect energization of said first named operator.

10. In combination with a refrigerant coil, an electrically operated fan for circulating air in contact with the coil, an electrically operated valve connected to the coil which when opened admits heated fluid into the coil, and an electrical system for controlling the operation of said fan and said valve comprising a circuit including the electrically operative portions of said fan and said valve, a two-position switch in said circuit which when in a first position energizes the operative portion of the fan and when in a second position energizes the operative portion of the valve, a normally closed switch in said circuit which when opened de-energizes the operative portion of the valve, means for biasing said switch to an open position, a latch for holding said switch closed, a relay connected to said latch which when energized moves the latch to permit the switch to open, a; condition responsive switch in said circuit and positioned in heat transfer relation-to'the coil and electrically connected to the relay for energizing the relay when the coil is heated, and a mechanical connection between the two-position switch and the normally closed switch for moving the latter to a closed position after the same has been opened.

11. A control device, comprising in combination, a relay having a movable armature, a switch positioned adjacent said relay, time controlled means for periodically moving said switch to a closed circuit position, a latching means extending between said switch and the armature of said relay in such a manner as to maintain said switch in a closed position when the armature is unattracted and to permit said switch to move to an open position when the armature is attracted, and means operated by said time control means for moving said latching means into its latched position when said switch is moved to a closed circuit position.

12. A refrigeration system comprising in combination, an evaporator, an electric valve for controlling the flow of a heated medium into said evaporator, said valve when moved to one of its positions initiating the fiow of said medium to said evaporator, timing means operably connected to said valve for periodically moving said valve 76 to said one position to permit defrosting moisture from said evaporator, a container positioned Idjacent said evaporator for receiving defrosted moisture from said evaporator, and an electrical heater associated with said container, said heater being energized by said timing means when said valve is moved to said one position.

13. In combination with a refrigeration system having a portion which accumulates ice, an electric heater associated with said portion for melting the accumulated ice, means for energizing said heater comprising a circuit adapted for connection to a source of power, a two-position switch in said circuit which when moved to one of its positions connects the heater and the source of power, a second switch in said circuit between the source of power and the heater which when opened Lie-energizes the heater, a relay operatively connected to said second switch 16 for eflecting opening of the same, and a third switch electrically connected to said relay which when closed energizes the relay to effect movement of the second switch to an open position to de-energize the heater.

FREDERICK M. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,022,469 Keighley Nov. 26, 1935 5 2,178,445 Warneke Oct. 31, 1939 2,281,770 Hoesel May 5, 1942 2,430,938 Leeson Nov. 18, 1947 

